Phosphate regime of sod-podzolic soil in natural and agrophytocenoses

The phosphate regime of sod-podzolic soil (heavy loam) of Cis-Urals under natural phytocenoses (mixed forest, cereal-grass meadow) and agrophytocenoses was studied. The influence of agricultural use of arable land on phosphate regime was evaluated in the long-term stationary experiment (year of establishment – 1978) and the eastern galega (Galega orientalis L.) (year of sowing – 1988). The total content of phosphorus in soil, quantity of its organic, mineral and plant available forms were studied, the fractional composition of mineral phosphates was considered (using Ginzburg-Lebedeva method). The total content of phosphorus in the upper soil layer in all studied objects varied from 1 030 to 1 350 mg/kg. Mineral phosphorus forms prevailed over organic ones in the soil. It was found that the fractional composition of mineral phosphates was 40–62% represented by iron phosphates and 31–48% by calcium phosphates, which is due to the characteristic features of the soil-forming rock – yellow-brown non-carbonate silt drape. Aluminum phosphates amounted to 8–12%. Long-term cultivation of crops during five cycles of the eight-field crop rotation led to a significant decrease in the content of organic phosphorus in the soil. The lower content of iron phosphates (1.6–1.8 times) and the higher content (1.3–2.0 times) of calcium phosphates, available for plants, were observed in the soil of long-term experiment when compared with natural phytocenoses. The content of plant available phosphorus in soil gradually decreased from 239 to 164 mg/kg from the moment of experiment establishment to the fifth rotation. Prolonged fertilizer application (N60P60K60) resulted in the significant increase in mineral and plant available phosphorus forms content in the soil. The residual phosphorus of fertilizers was noted in the Fe-P, Ca-PI and Ca-PII fractions. Under the eastern galega the quantitative and qualitative indicators of the phosphate regime of the soil did not differ significantly from their natural analogues.

Effect of magnetic iron-zirconium modified zeolite on the different phosphorus forms in river sediment under aerobic and anoxic condition

In this study, a magnetic iron-zirconium modified zeolite (FeZrMZ) was synthesized. Through sediment culture experiments, the influence of the addition of modified materials on the migration and transformation of phosphorus in river sediments was investigated. The results show that the modified zeolite can not only effectively reduce the phosphorus concentration in the overlying water, but also significantly reduce the phosphorus concentration in the pore water of sediments. The addition of modified zeolite makes the unstable weakly adsorbed phosphorus (NH4Cl-P) and redox phosphorus (BD-P) transform into the more stable metal oxide bound phosphorus (NaOH-P) and very stable residual phosphorus (Res-P).The four types of bioavailable phosphorus (BAP), including water-soluble phosphorus (WSP), readily desorbable phosphorus (RDP), algae-available phosphorus (AAP), and NaHCO3 extractable phosphorus (Olsen-P). Under anoxic conditions, they were reduced by 53.5%, 14.1%, 23.8%, and 49.9% respectively. Under aerobic conditions, they were reduced by 23.2%, 16.6%, 32.1%, and 50.0%. Obviously, the addition of magnetic iron-zirconium modified zeolite can reduce the release potential of phosphorus in sediment, and it can be recovered through the action of an external magnetic field, so it can be used as an effective sediment modifier to control the sediment the release of phosphorus.

Effect of organic loading on phosphorus forms transformation and microbial community in continuous-flow A2/O process

A continuous-flow Anaerobic/Anoxic/Oxic (A2/O) system was operated at different organic concentrations to systematically investigate the effect on the nutrient removal, secretion characteristics of extracellular polymer, phosphorus forms transformation and changes in functional flora in this system. The results showed that high organic loading was more conducive to promote the secretion of extracellular polymeric substance (EPS), the increase of polysaccharide content was more obvious compared with protein, the impact of organic loading on the components of loosely-bound EPS (LB-EPS) was higher than that of tight-bound EPS (TB-EPS). Phosphorus in sludge floc mainly existed in the form of inorganic phosphorus (IP), and IP mainly existed in the form of apatite inorganic phosphorus (AP). High organic load showed higher phosphorus storage in EPS, and the phosphorus content in EPS was positively correlated with the content of EPS. Non-apatite phosphorus (NAIP) content played an important role in the extracellular dephosphorization. The abundance of Nitrosomonas and Nitrospira responsible for nitrification decreased with the increase of organic loading. The group of denitrifiers was large, and Azospira was the most abundant genus among them. Dechloromonas, Acinetobacter, Povalibacter, Chryseolinea and Pirellula were the functional genera closely associated with phosphorus removal.